How do I Measure my Roof?

To find how much roofing material you need to buy when re-roofing or roofing a new roof, you will have to measure your roof accurately. You don't want to overspend by buying too much. Since shingles may need to match in color, buying too little could result in mismatched coloring because of varying lot numbers that will not look very attractive.

To find the total square footage of your roof, you will measure each plane or gable individually. If it is a single plane, you simply measure and multiply the length by the width to get the square feet. For example, if a single plane is 100 ft. long and 150 ft. wide, you would multiply 100 X 150 to get 15,000 square feet. Measuring the other side, you find the same figures, so you add the two planes together for a total of 30,000 square feet.

If your roof has multiply planes and/or gables, you use the same method. Measure each area individually and add all of them together for the total square footage.

If your roof is extremely steep, you can use a method that will not require your being on the roof's steep slope. To get the length, measure the outside wall and add the length of the overhang. To determine the width, throw a rope over the ridge to the opposite eave and mark the rope at both eaves. Divided in half, this will equal one side's width.

To figure the slope of your roof, you will measure how much the roof rises vertically in a horizontal 12 inches. For example, if in a 12 inch distance the roof rises four inches, you will have a slope of 4 in 12.

Now, how does all this translate to the purchase of roofing material? Generally, the roof measurements are converted to what is called "squares." A square equals one 100 square ft. area. To determine the squares needed to shingle the roof, you divide your total square footage by 100. In our example that would be 30,000 sq. ft. divided by 100 to get 300 squares. This means you will need to buy 300 squares of shingles to cover our sample roof. Typically, one square of shingles will contain three bundles. If you need the underlayment for a new roof, those rolls come in four squares per roll, so you would need 75 rolls of underlayment for this sample roof. To be safe, you should always add an extra 10% to all of your materials to allow for trimming or mistakes.

To measure how many nails you need, use the general rule of four nails per shingle. This would equal 320 nails per square with the average 80 shingles per square. High wind areas or special types of shingles may require six or more nails per shingle. You should read the shingle packaging to be sure how many you should use.

Measuring your roof for your materials is not really that difficult. You just need simple math equations to convert the raw measurements into squares. It may be a good idea to measure twice and to have someone go over your figures with you to catch any mistakes that you might have made.

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